The Secret Gospel of Mark refers to a non-canonical gospel which is the subject of the Mar Saba letter, a previously unknown letter attribute to Clement of Alexandria which Morton Smith claimed to have found transcribed into the endpapers of a 17th century printed edition of Ignatius. The authenticity of this letter remains in dispute. The manuscript and the book where it was found have disappeared; all that remains are photographs made by Professor Smith in 1958 and by other scholars in 1976.